Additive for solid hydrocarbon fueled direct fired burners, furnaces, open flames and related processes

ABSTRACT

The present invention relates to the field of fuel additives for hydrocarbon fuels that acts to enhance efficiency and/or reduce pollution. The fuel additive is a phosphorus-containing composition that can be added to the surface of solid hydrocarbon fuels for combustion with the fuel in a direct fired burner, furnace or open flame.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to provisional patent application 60/628,002 filed Nov. 15, 2004.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to the field of fuel additives, in particular, to an additive for solid hydrocarbon fueled burners, furnaces and flames to enhance efficiency and/or reduce undesirable emissions, such as pollutants.

BACKGROUND OF THE INVENTION

Solid hydrocarbon fuels, such as coal, have long been used to fuel burners, furnaces and open flames. Coal, particularly lignite and other low BTU coals, does not burn very efficiently and generates considerable smoke, NOx, SO₂, particulate matter and other undesirable emissions including CO. Chemical compounds have been used as combustion improvers to enhance combustion efficiency, of solid fuels. However, many of these additives contain heavy metallic elements such as manganese, zinc, iron, copper, cerium, calcium and barium. On burning, some of these elements can produce heavy metal solid residues, which are highly undesirable.

A fuel additive that includes a combustion catalyst to reduce smoke and particulate emissions from coal fired burners, furnaces and other direct-fired applications would be advantageous. A fuel additive that increases efficiency and/or decreases pollutants for coal and other solid fuels including low quality coal such as lignite, used in these applications would be particularly advantageous. It would also be advantageous to reduce smoke, particulate and nitrogen-containing emissions from fuel applications. In addition to reduction of NO_(x), reduction or elimination of other toxic pollutants, such as SO₂ are highly desirable. An additive that does not result in the formation of heavy metal precipitates and residues during the combustion process would be desirable.

SUMMARY OF THE INVENTION

The present invention includes a fuel additive and a method of using the additive in relation to solid fuels, such as coal.

The fuel additive of the invention includes a phosphorus-containing parent solution containing [Y]_(x)H₂PO₄, [Y]_(x)+HPO₄, where Y is a cation. Y does not have to be the same cation in both salt compounds. The cationic portion of the salt components can be any cation, with potassium being a preferred cation. In this case, the preferred components would be KH₂PO₄, K₂HPO₄. These salts are at least partially dispersed in water or other appropriate solvent to create the phosphorus-containing parent solution. Advantageously, this embodiment of the fuel additive is an ammonia-free solution. One preferred embodiment includes adding these components, in the presence of water, to create the phosphorus-containing parent solution as an aqueous parent solution. The water acts as the solvent. Other preferred parent solution solvents include alcohols. Another group of preferred cations would be the alkali metals or Group 1A elements. While NH₄ used as Y creates a fuel additive that enhances fuel performance, there are instances when it is preferred to avoid ammonium and thereby ammonia altogether.

Another preferred embodiment of the phosphorus-containing parent solution includes the addition of [NH_(4]2)HPO₄ to the [Y]H₂PO₄, [Y]_(x+)HPO₄, and water. Yet another embodiment includes the addition of NH₄C₂H₃O₂ where C₂H₃O₂ ⁻ ion is an acetate group such that the solution contains [Y]_(x)H₂PO₄, [Y]_(x+)HPO₄, [NH₄]₂HPO₄, NH₄C₂H₃O₂ and water. When the fuel additive is prepared using ammonium compounds, ammonium compounds being defined as those compounds containing NHx groups, the nitrogen in the solution is essentially all in the form of ammonium ions. There is at most a negligible amount of free ammonia. In a preferred embodiment, the solution has a pH between about 6.0 and 8.0.

Another preferred embodiment of the phosphorus-containing parent solution includes the addition of [Y] _(x)PO₄ to the [Y]_(x)H₂PO₄, and [Y]_(x+)HPO₄.

While orthophosphoric acids have been described, also called phosphoric acids, this includes pyrophosphoric acids, which are the condensed analogs of orthophosphoric acid. The difference being that, through the process to condense the orthophosphoric acid, the PO₄ ³⁻ becomes P₂O₇ ²⁻ or other condensed phosphates. Therefore, [Y]_(x)H₂PO₄, and [Y]_(x+)HPO₄ are precursors to pyrophosphoric acids. The use of the pyrophosphoric and other condensed forms is therefore encompassed within the definition of the orthophosphate form.

In the case of solid fuels, such as coal, the phosphorus-containing parent solution can be applied directly to the solid fuel in any manner capable of producing a uniform coating, such as spraying, dipping, slurring or the like. In many instances in industry, coal is sprayed with water to prevent dust formation in the grinding process prior to combustion. The phosphorus containing parent solution can advantageously be included with this water spray. However, other methods known in the art to contact an aqueous solution with the solid hydrocarbon can also be used.

The fuel additive of the invention is useful to enhance combustion such that more complete combustion is achieved with increased combustion to CO₂ and H₂O as compared to the combustion of the solid fuel without the fuel additive. The outcome is the reduction of products of partial combustion as well as NO_(x), thereby increasing fuel efficiency.

The fuel additive is used by adding this additive to the fuel in an amount sufficient to increase fuel efficiency or to reduce pollutants. The terms enhanced and enhanced combustion refer to either of these effects. An example of reduced pollutants is a reduction of NOx in an exhaust gas produced from a solid fueled direct fired burner, furnace or open flame. Advantageously, both of these effects are observed though the addition of the fuel additive of the current invention. A preferred embodiment includes the addition of between about 50 and 150 ppm phosphorus onto the fuel though the addition of the fuel additive. Increased amounts of phosphorus are effective as well.

Included in the invention is a process for enhancing fuel performance of a solid hydrocarbon fuel in a combustion system including the steps of providing the fuel additive described above in an amount effective to enhance fuel performance to the solid hydrocarbon fuel and combusting the solid hydrocarbon fuel with the fuel additive. The combustion system can be any means known to those with ordinary skill in the art for combusting solid hydrocarbons. The combustion system can include one or more direct fired burners, furnaces, fluidized beds, open flames or the like. In a preferred embodiment, this process is used with a solid hydrocarbon fuel. The result of adding the additive to the solid hydrocarbon fuel is an enhanced fuel that has a substantial amount of solid hydrocarbon fuel suitable for combustion, and an amount of the fuel additive operable to enhance combustion. Preferably, the enhanced fuel contains phosphorus in an amount operable to reduce emissions upon combustion of the enhanced fuel as compared to the combustion of the hydrocarbon fuel without the fuel additive. More preferably, the enhanced fuel contains phosphorus of between about 1 and 150 ppm by weight. Another preferred embodiment is between about 1 and 80 ppm by weight.

In a fluidized bed application, the fuel additive can be introduced onto the coal prior to burning, onto fly ash prior to a secondary burning or can be injected into the fluidized bed or partially fluidized bed during the combustion process by means known in the art.

An alternate embodiment of the invention includes a process for enhancing fuel performance of a hydrocarbon fuel in a combustion system including the steps of adding a chemical addition composition to the hydrocarbon fuel in an amount effective to enhance fuel performance. The chemical addition composition is created by (i) mixing in an aqueous medium a source of reactive NH₂ groups with one of the following:

1. (a) an alkali metal hydroxide to raise the pH of the solution above 12 to form an aqueous ammonium/alkali metal hydroxide; or

2. (b) a source of phosphoric acid to lower the pH of the solution to about 0 to form an acidic ammonium mixture.

3. The next step includes either combining the intermediate solution of step (i.a.) with the source of phosphoric acid; or the solution of (i.b.) with the hydroxide at a rate sufficient to create a highly exothermic reaction. This results in reactive NH₂ groups being contained in solution during the formation of the chemical addition composition. This chemical addition composition is added to the hydrocarbon fuel.

The parent solution, or the chemical addition composition of the invention, can be added directly onto a solid hydrocarbon combustion fuel.

An enhanced fuel is created when a substantial amount of a solid fuel suitable for combustion is combined with an amount of the phosphorus-containing parent solution or the chemical addition composition sufficient to reduce emissions or to increase efficiency upon combustion of the enhanced fuel.

A composition of phosphoric acid, alkali metal hydroxide and a source of reactive NH₂ groups has been explored in U.S. Pat. No. 5,540,788 for the creation of a conversion surface, the disclosure of the patent being incorporated herein by reference. The current invention includes the use of the conversion surface composition as a solid fuel additive. In one embodiment the fuel additive is chemical addition composition for the enhancement of hydrocarbon fuels where the chemical addition composition has the composition disclosed in U.S. Pat. No. 5,540,788. This embodiment is unique in the use of the source of reactive NH₂ groups, which can be advantageous under certain circumstances. While the chemical composition including reactive NH₂ groups has certain advantages, it can result in the presence of free ammonia. Various other embodiments of the fuel additive of this invention avoid the production of free ammonia and the related issues.

DETAILED DESCRIPTION

The fuel additive of the invention is believed to perform a gas phase conversion of hydrocarbon fuels to achieve more complete combustion to CO₂ and H₂O in the process. Preferably, the fuel additive is provided as an aqueous parent solution that can be added directly to the surface of the solid fuel. The mechanism of addition of the aqueous parent solution to the solid surface is not critical as long as a reasonably uniform dispersion on the solid surface is obtained. In some cases, it may advantageous to include dispersants, surfactants or other surface active agents to help provide a uniform dispersion of the additive on the solid surface. In these cases it is the usual practice to dissolve, disperse or emulsify the surface active additive in the parent solution. However, pre-coating the solid surface with the surface active agent is also conceivable. Tests run using infrared and other testing techniques confirm the reduction of CO from the offgas from the combustion of solid hydrocarbon fuels with the fuel additive of the invention.

The invention includes the use of the fuel additive in the direct-fired burners, furnaces and open flames. This is believed to be particularly valuable for burners and furnaces using low BTU and/or high sulfur coals. Use in the burner, furnace or flame appears to provide combustion benefits allowing for a reduction in particulate and other emissions. The process of the invention is effective at the high temperatures produced as part of the combustion process such that the fuel additive is contained in the flame with the fuel. Examples of the use of coal are too numerous to mention but, the use of the additized coal in electric generation plants in which the quality of the coal can vary significantly, especially with respect to BTU and sulfur content, is particularly advantageous.

One example of a preferred formulation of the invention includes the following ratios: 1.597 mols KH₂PO₄, 0.693 mol K₂HPO₄, 0.315 mol [NH₄]₂HPO₄ and water. The pH of the solution can be controlled through manipulation of the ratios of these components. By manipulating the ratios of the resulting H₂PO₄ ⁻ and HPO₄ ²⁻ ions, the solution can be created in a preferred pH range of about 6.0 to about 8.0.

In a preferred embodiment, KH₂PO₄, K₂HPO₄, [NH₄]₂HPO₄ and water are created into the phosphorus containing parent solution. One example of a preferred embodiment is 0.3 wt % phosphorus in the solution, which can be added directly to the solid fuel surface in a suitable manner. Upon addition to the fuel surface, the phosphorus content can be in the range of 5-100 ppb and still be effective. Preferably, 1-250 ppm phosphorus is used on the fuel. Higher amounts are also effective. More preferably, 1-150 ppm phosphorus by weight of the total solid fuel weight on the surface of the solid fuel. Another preferred embodiment is 1-80 ppm phosphorus.

An example of an alternate embodiment of the phosphorus-containing parent solution that is for use on a solid fuel includes mixing about 2.6 molar (M) orthophosphate with alkali metal and ammonium cations, the resulting aqueous parent solution having a pH of 7 at ambient temperatures. The aqueous parent solution prepared in this fashion, when added to the solid fuel, acts to diminish the emission of pollutant molecules, under normal operating conditions. An example of an alternate embodiment includes the use of phosphoric acid, potassium hydroxide, ammonium hydroxide in water. Acetic acid can also be added. The amounts of the components can be adjusted to reach the desired pH.

EXAMPLE 1

1. Prepare a Phosphoric Acid/Acetic Acid solution [H₃PO₄/HOA_(c) Solution]. For this run, the H₃PO₄/HOA_(c) Solution is about 90% mole of H₃PO₄ and 10% mole of HOA_(c).

2. Prepare for reaction De-ionized water

3. 2,736.39 lbs of the Potassium Hydroxide is added to the water

4. Add to this aqueous solution 1315.14 lbs of the Ammonium Hydroxide (29%)

5. Into the resulting solution, add the H₃PO₄/HOAc Solution and allow for reaction.

6. After reaction, adjust pH with acetic acid to a pH of about 7.0. The resulting product of this reaction is useful as the chemical addition component to enhance hydrocarbon fuel.

EXAMPLE 2

Use of the fuel additive described in Example 1 in combination with a 300 mesh high sulfur Ohio composite coal, containing 3.4% S in provided a 39% reduction in CO emissions in the exhaust gas as compared to the coal without the fuel additive, 52% reduction in SO₂, reduction in NOx and 10% reduction in particulates. The coal was impregnated with the aqueous parent solution, prior to combustion, such that the resulting P concentration (based on total weight of coal) was 80 ppm.

EXAMPLE 3

Unit Ratio Component Lbs weight Phosphoric Acid 2,583 0.25 Potassium Hydroxide 2,736 0.26 Ammonium Hydroxide 1,315 0.13 Acetic Acid 672 0.06 Deionized Water 3,105 0.30 Total Phosphorus-Containing Parent Solution 10,411 1.00

In an alternate embodiment, the solvent is one that is defined by solubility or dispersibility of the salts in the solvent as well as the volatility of the solvent. For example, the salts are preferably dispersed throughout the solvent but the solvent is of such volatility that it can be vaporized during the combustion process without affecting the quality of the combustion.

While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention. For example, [Y]_(x)H₂PO₄, [Y]_(x+)HPO₄ also encompasses [Y]_(x)[H₂PO₄]_(z), [Y]_(x)+[HPO₄]_(z) where x and z are variable integers. 

1. A process for enhancing fuel performance of a hydrocarbon fuel in a combustion system having a direct fired burner, furnace or open flame comprising the steps of: providing a fuel additive to the hydrocarbon fuel in an amount effective to enhance fuel performance to the direct fired burner, furnace or open flame and combusting the hydrocarbon fuel with the fuel additive, the fuel additive comprising a mixture of salts and a dispersion fluid, the mixture of salts comprising: [Y]_(x)H₂PO₄; and [Y]_(x+)HPO₄, wherein [Y] is a cation, the dispersion fluid being operable to maintain the salts within the dispersion fluid in at least a partially dispersed state to create a solution, the enhanced fuel performance being measurable by increased fuel efficiency or decreased pollutant output in an exhaust gas resulting from the combustion of the fuel and the fuel additive.
 2. The process of claim 1 for enhancing fuel performance wherein the fuel additive is ammonia-free.
 3. The process of claim 1 for enhancing fuel performance wherein the fuel additive further comprises [NH₄]₂HPO₄.
 4. The process of claim 1 for enhancing fuel performance wherein the fuel additive further comprises NH₄C₂H₃O₂ where C₂H₃O₂ is an acetate group.
 5. The process of claim 1 for enhancing fuel performance wherein the pH of the solution is between about 6.0 and 8.0.
 6. The process of claim 1 for enhancing fuel performance wherein phosphorus is present in the hydrocarbon fuel in an amount of between about 1 and 150 ppm by weight.
 7. The process of claim 1 for enhancing fuel performance wherein the hydrocarbon fuel is a solid hydrocarbon fuel, preferentially coal, more preferentially high sulfur coal and most preferentially high sulfur and low BTU coal.
 8. A process for creating an enhanced hydrocarbon fuel for use in a combustion system comprising the step of adding an amount effective to enhance fuel performance to the hydrocarbon fuel of a chemical addition composition, the chemical addition composition comprising reaction products from mixing of a source of phosphoric acid, an alkali metal hydroxide, ammonium hydroxide and water.
 9. The process of claim 8 for creating an enhanced hydrocarbon fuel wherein the chemical addition composition further comprises acetic acid.
 10. A process for creating a fuel additive for enhancing combustion of a hydrocarbon fuel, the process comprising the step of: mixing the salts [Y]_(x)H₂PO₄ and [Y]_(x+)HPO₄, wherein [Y] is a cation, in a solvent to at least partially disperse the salts in the solvent to create an phosphorus-containing parent solution that is operable to enhance combustion when added to a direct fired burner, furnace or open flame in the presence of a solid hydrocarbon fuel and combusted.
 11. A combustion additive comprising a mixture of salts and a dispersion fluid, the mixture of salts comprising: [Y]_(x)H₂PO₄; and [Y]_(x+)HPO₄, wherein [Y] is a cation, the dispersion fluid being operable to maintain the salts within the dispersion fluid in at least a partially dispersed state to create a solution, the fuel additive being operable to enhance combustion when placed into contact with fuel in a direct fired burner, furnace or open flame and combusted, the enhanced combustion being measurable by increased fuel efficiency or decreased pollutant output in an exhaust gas resulting from the combustion of the fuel and the fuel additive.
 12. The fuel additive of claim 11 further comprising [NH₄]₂HPO₄.
 13. The fuel additive of claim 11 further comprising NH₄C₂H₃O₂ where C₂H₃O₂ is an acetate group.
 14. The fuel additive of claim 11 wherein the pH of the solution is between about 6.0 and 8.0.
 15. An enhanced fuel comprising a substantial amount of solid fuel suitable for combustion and an amount of fuel additive, of claim 11, operable to enhance combustion.
 16. The enhanced fuel of claim 15 wherein phosphorus is present in the hydrocarbon fuel in an amount of between about 1 and 150 ppm by weight.
 17. The enhanced fuel of claim 15 wherein the amount of fuel additive is the amount operable to reduce emissions upon combustion of the enhanced fuel as compared to the combustion of the hydrocarbon fuel without the fuel additive. 